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🧮 BG1SB EFHW · ATR-1000 Tuner Parameter Calculator

Data baseline: measurements of 2026-09-27/28 (bypass sweeps + device tunes + relay cross-probing). Model and formulas at the bottom of the page.

Frequency input

MHz 80m 60m 40m 30m 20m 17m 15m 12m 10m

Antenna impedance model curve (piecewise-linear interpolation between measured anchors)

Model anchor table (data sources and confidence)

Measured confirmed by both device tune and relay cross-probing; Back-derived inverted from learn-library L/C under a perfect-match assumption; accuracy limited by achieved SWR>1.0 and meter quantisation; Weak few samples, reference only.

Derivation: from relay codes to antenna impedance

1. ATR-1000 hardware abstraction. Inductance: 8-bit binary relays (0.1 µH steps, ind∈[0,127] → L=ind×0.1 µH); capacitance: 7-bit (10 pF steps, cap∈[0,127] → C=cap×10 pF); sw selects which side the capacitor hangs on: sw=0 "LC" = series L + shunt C on the load (antenna) side; sw=1 "CL" = shunt C on the source (rig) side + series L. The topology orientation was determined by relay cross-probing (at the L44/C34 point: LC model predicts 1.81 / CL model predicts 4.6 / measured 2.32).

2. Forward problem (given antenna impedance Z=R+jX, find the tuned input impedance).

LC: Z_in = jωL + 1 / (1/Z + jωC)
CL: Z_in = 1 / (1/(jωL + Z) + jωC)
Γ = (Z_in − 50)/(Z_in + 50)，SWR = (1+|Γ|)/(1−|Γ|)，ω = 2πf

3. Inverse problem (given the L/C that achieved a match, find the antenna impedance). Solve with Z_in=50:

LC: 1/Z = 1/(50 − jωL) − jωC
CL: Z = 1/(1/50 − jωC) − jωL

The inverse assumes a "perfect match", but real learn records show achieved SWR of 1.0–1.6, so the inverted value lies on a constant-SWR contour rather than an exact point — the exact point needs joint constraints of "bypass SWR magnitude + measured SWR with several relay settings" (the 5.3515 MHz anchor on this page was fixed at 59+j112 by a 4-constraint least-squares fit).

4. Calculator solve. For the input frequency, R and X are each linearly interpolated between adjacent anchors to give Ẑ; then all 2×128×128 combinations of (sw, ind, cap) are brute-forced and the one with the lowest tuned SWR wins. The runner-up topology is shown alongside for comparison.

Model boundaries (important — do not blindly trust)

⚠️ Interpolation in anchor-free frequency ranges (especially 3.9–5.3 MHz, 8–10 MHz, 16–18 MHz, 22–24 MHz) can get even the sign of the reactance wrong — the 60 m measured lesson: two polynomial fit families both guessed capacitive across the data gap, while the measurement was inductive +112 Ω; tuning per the fit would land at SWR 22+. This calculator flags low confidence for frequencies far from anchors; in that case use the panel Tune button and let the device measure (confirmed learning will automatically enter the library and correct it).

· All anchors are dry-weather baselines; rain makes SWR drift substantially in anti-resonant regions such as 17 m (2026-09-27 19:09 18.1 MHz bypass=12.56 vs the ≈5 measured that night at 00:11 — inconsistent because the weather state changed).
· The ATR meter is quantisation-compressed at the low-SWR end (readings generally 0.1–0.2 below the model); SWR=1.00 is the range floor.
· Inverted-Z uncertainty is about ±5 Ω/±15 Ω (R/X), mapping to roughly ±3 steps/±5 steps in L/C; so treat calculated values as a tuning starting point — final parameters come from the device's own sweep + measurement.

BG1SB · EFHW 21 m · 49:1 (2:14) 2643251002 · ATR-1000 · data baseline 2026-09-28 · Back to the antenna deep dive